1. Field of the Invention
The present invention relates to an apparatus for and method of welding a spacer grid, and more particularly, to an apparatus and method for capturing an image of a welding spot during a welding task and determining an accurate position of the welding spot based on the captured image in order to perform an accurate welding task.
2. Background of the Related Art
In recent years, a spacer grid used to support and fix a nuclear fuel is formed in a lattice shape by intersecting long plates, which are generally made of zirconium, vertically and horizontally and then performing welding, as disclosed in Korean Patent Application No. 10-1983-0004399. More specifically, each of the plates has grooves formed therein for accommodating the plates that cross each other at right angles. The grooves are fixed in such a manner that they are coupled to one another, and intersections of the plates that cross each other at right angles are then welded to thereby form a spacer grid.
It has been known that defects of a spacer grid during its fabrication includes defective material of plates constituting a spacer grid, fixing defects of plates before welding, laser defects upon welding, fixing defects of retention straps for fixing plates constituting a spacer grid upon welding task, and so on. It has been known that if the several defects occur in combination, it results in welding defects of the spacer grid.
There may be several methods for minimizing the welding defects of the spacer grid depending on various causes. Among them, it is most important to accurately find the intersections of the plates that are orthogonal to one another, which become welding spots, before welding, accurately check the welding state after welding, and then weld spots that have not been properly welded so as to minimize the occurrence of these defects. In particular, when the grooves for inserting the orthogonal plates thereto are inserted into the plates constituting the lattice, there is generated some clearance. Thus, the entire welding spots are not formed regularly and have some error. It is therefore more important to know an accurate position of a welding spot in advance.
In order to prevent the welding defects, in recent years, an image of a spacer grid is captured before a welding task in order to grasp overall welding spots to thereby perform the welding task. A welding state is checked manually after the welding task and a welding task is then re-performed on a defective spacer grid again.
However, this method is problematic in that the time taken before the welding task of the spacer grid is lengthened and it cannot cope with welding defects immediately, thereby decreasing work efficiency.
Meanwhile, the spacer grid is welded at a temperature of 3000° C. or higher using a laser, which is very higher than that of general arc welding. Thus, in order to save the time taken for a welding task, if an image of the spacer grid is captured during or right after the welding task, a hot spot phenomenon in which the image is interfered due to the high temperature is generated. It makes it difficult to read the image. In other words, in order to enhance the efficiency of the welding task of the spacer grid, there is a need for a technique for removing or minimizing hot spots from an image during or right after a welding task.